#include <iostream>
#include <cmath>
using namespace std;
int main()
{  
    double x, y;
    while(cin>>x>>y)
    {
        if(abs(x)<1e-6 || abs(y)<1e-6) break;
        cout<<"average:"<<2.0*x*y/(x+y)<<endl;
    }
    return 0;
}